NAME

     rlogind — remote login server

SYNOPSIS

     rlogind [-afhlLn]

DESCRIPTION

     Rlogind is the server for the rlogin(1) program.  The server provides a remote login
     facility with authentication based on privileged port numbers from trusted hosts.

     Options supported by rlogind:

     -a      This option exists for compatibility with historical systems.

     -f      Disable the Nagle algorithm.  This is only needed to work around some broken
             operating systems.

     -h      Permit use of superuser “.rhosts” files.

     -l      Prevent any authentication based on the user's “.rhosts” file. If the user is
             logging in as the superuser and the -h option is used, “.rhosts” processing is still
             enabled.

     -L      Prevent any authentication based on “.rhosts” or “hosts.equiv” information.

     -n      Disable keep-alive messages.

     The -h, -l, and -L flags are not used if PAM (Pluggable Authentication Module) support is in
     use.

     The -h and -l options should also not be trusted without verifying that they work as
     expected with the particular version of libc installed on your system (and should be tested
     again after any libc update) because some versions of libc may not honor the internal flags
     used by rlogind.  As the -L option bypasses the libc functions entirely, it is not subject
     to this problem.

     Also note that the design of the .rhosts system is COMPLETELY INSECURE except on a carefully
     firewalled private network. Always use the -L option under all other circumstances. Also,
     since rlogind does not encrypt communications, it should not, in general, be used at all.
     Consider ssh(8).

     Rlogind listens for service requests at the port indicated in the ``login'' service
     specification; see services(5).  When a service request is received the following protocol
     is initiated:

     1.   The server checks the client's source port.  If the port is not in the range 512-1023,
          the server aborts the connection.

     2.   The server checks the client's source address and requests the corresponding host name
          (see gethostbyaddr(3), hosts(5) and named(8)).  If the hostname cannot be determined,
          the dot-notation representation of the host address is used.  The addresses for the
          hostname are requested, verifying that the name and address correspond.  Normal
          authentication is bypassed if the address verification fails.

     Once the source port and address have been checked, rlogind proceeds with the authentication
     process described in rshd(8).  It then allocates a pseudo terminal (see pty(4)), and
     manipulates file descriptors so that the slave half of the pseudo terminal becomes the
     stdin, stdout, and stderr for a login process.  The login process is an instance of the
     login(1) program, invoked with the -f option if authentication has succeeded.  If automatic
     authentication fails, the user is prompted to log in as if on a standard terminal line.

     The parent of the login process manipulates the master side of the pseudo terminal,
     operating as an intermediary between the login process and the client instance of the rlogin
     program.  In normal operation, the packet protocol described in pty(4) is invoked to provide
     ‘^S/^Q’ type facilities and propagate interrupt signals to the remote programs.  The login
     process propagates the client terminal's baud rate and terminal type, as found in the
     environment variable, ‘TERM’; see environ(7).  The screen or window size of the terminal is
     requested from the client, and window size changes from the client are propagated to the
     pseudo terminal.

     Transport-level keepalive messages are enabled unless the -n option is present.  The use of
     keepalive messages allows sessions to be timed out if the client crashes or becomes
     unreachable.

DIAGNOSTICS

     All initial diagnostic messages are indicated by a leading byte with a value of 1, after
     which any network connections are closed.  If there are no errors before login is invoked, a
     null byte is returned as in indication of success.

     Try again.
             A fork by the server failed.

SEE ALSO

     login(1), ruserok(3), rshd(8)

BUGS

     The authentication procedure used here assumes the integrity of each client machine and the
     connecting medium.  This is insecure, but is useful in an ``open'' environment.

     A facility to allow all data exchanges to be encrypted should be present.

     A more extensible protocol should be used.

HISTORY

     The rlogind command appeared in 4.2BSD.